Generally speaking, liquid chromatography is a method for separating, or purifying different chemical compounds. The compound is referred to as the analyte, and the liquid that is forced through the column is referred to as the eluant. The separation is based on the different properties possessed by the compounds, such as molecular weight, affinity for certain solid supports, ionic properties, etc.
The use of certain devices attached to a liquid chromatography column to detect various chemical species once they have been separated by the column is well known in the prior art. For example, universal detectors based on a change in the index of refraction of the eluant or change in the dielectric constant are used. More specific detectors that respond to ultraviolet absorption, fluorescence, or electrolytic properties of the analyte are also in common use.
The prior art, however, does not contain a detecting device that responds to changes in the surface tension of the eluant caused by the presence of an analyte. It is well known that the surface tension of a liquid is changed dramatically when certain compounds, which are sometimes referred to as surfactants, are dissolved in the liquid. An example is the lowering of the surface tension of water by soap. Lowering of the surface tension, in effect, allows the liquid to wet more easily a material with which it is in contact. The phenomenon of surface tension reduction resulting from change in the composition of a solvent is quite general and applies to both soluble solids and liquids that are added to a solvent. Some coupounds are notable in that they produce very sizeable changes in the surface tension.